 Hi, you guys. So we're back today to talk about the immune system. We spent a little bit of the last lecture on blood talking about the immune system. We talked about blood typing, and it was kind of a nice introduction to the immune system because we talked about antigens and how antigens are basically any substance that can stimulate an immune response. And we had a little bit of conversation about antibodies as well. So we'll see more from antibodies in this lecture and the next lecture, but there are two branches of the immune system. And the bottom line with the immune system, not surprising at all, it's identifying and attacking non-self, you. And the immune system will take care of that for you. So there are two branches of the immune system, and today we're going to talk about one of them. It's the innate immune system. And tomorrow, or whatever day it is, we're going to talk about the acquired. And I'm just going to do a really quick compare and contrast and carry out strategies to kill non-self. The innate immune system, however, is present from birth. That means you come out of your mama's belly ready to attack things that aren't you. Acquired immune system, you have to. Where'd that thing come from? Doing weird things. The acquired immune system is acquired. I'm going to write that down because it requires time to get the strategies that are employed with the acquired immune response. The innate immune response is fast. That's what the acquired immune response is, slow. The acquired immune response has memory, which means even though it's slow, there is a memory that allows it to basically hang on to strategies. It took time to develop the strategy to attack the bad guy, but once you have the strategy, then you're going to remember it that you can attack that bad guy again. And along those lines, the acquired immune response is very, very specific. And what that means is that a bad guy, an antigen, something that stimulates the immune response, is the acquired immune response to a very specific antigen. So basically, there's like a million different possible responses, and each part of the acquired immune response is only going to respond to one antigen and only that one specific antigen, whereas the innate immune response is totally general. So it has like, I don't know, five strategies, not a million, five. It uses the same strategy against all the bad guys. So one of the strategies is inflammation. And we're going to spend the first inflammation, we're going to spend the first chunk of this lecture talking about inflammation. What is it? And why is it? But it's a very generalized response to an invader. Acquired immune response is much more specific than that. I think that's a pretty good overview. So let's talk about inflammation because it's actually really cool.